1. Field of the Invention
The present invention relates to an inverter system for a vehicle-mounted air conditioner.
2. Description of the Related Art
A motor for driving a compressor that constitutes a vehicle-mounted air conditioner is controlled in operation by an inverter system.
As shown in FIG. 2, a conventional inverter system 1 operates at a low voltage of about 5 V or 15 V converted by a non-isolated DC-DC converter 4 from a high voltage of 100 V or more supplied from a high voltage power supply 3 for driving a motor 2. The inverter system 1 communicates with a host ECU 6 via a communication interface 5 for controlling a vehicle-mounted air conditioner or the like. Other electrical equipment systems of a vehicle including the host ECU 6 for the inverter system 1 or the like operates at a voltage of 12 V or 24 V supplied from a vehicle-mounted battery power supply 7. The high voltage for driving the motor 2 being applied to the other electrical equipment systems for some reasons may lead to a failure, and thus the inverter system 1 and the other electrical equipment systems can communicate with each other while being isolated by an isolated communication connector 8 such as a photocoupler (for example, see Japanese Patent No. 3351330).
In the above described configuration, a GND (ground) potential of a control circuit such as a control microcomputer 9 that constitutes the inverter system 1 has the same potential as a GND potential of a high voltage system for driving the motor 2, and is isolated from GND of the vehicle-mounted battery power supply 7. However, the high voltage system is used for driving the motor 2, and thus a voltage and a current significantly changes, which may cause noise in the control circuit such as the control microcomputer 9.
GND of the communication interface 5 that communicates with the inverter system 1 is isolated from the GND of the control microcomputer 9, and communication between the communication interface 5 and the control microcomputer 9 is performed via the isolated communication connector 8 such as a photocoupler. Thus, the communication speed is limited by responsivity of the photocoupler used or the like, thereby preventing precise control.
The present invention is achieved on the basis of such technical problems, and has an object to provide an inverter system for a vehicle-mounted air conditioner that prevents noise from entering a control circuit and allows more precise control by high speed communication.